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Servlet, JSP
Margus Hanni, Nortal AS
11.03.2013
Viited varasematele
materjalidele…
2012 – TÜ - Servlets, JSP, Web
Containers – Roman Tekhov
2010 – Webmedia - Java EE +
containers – Anti Orgla
Kas on asjakohane?
http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html
Kas on asjakohane?
http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html
Hello World - C ja JAVA
#include <stdio.h>
int main() {
printf("Hello World\n");
return 0;
}
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World");
}
}
Kas on asjakohane?
Võrreldes eelmise aastaga on JAVA
populaarsus taas kasvanud
Jätkuvalt on JAVA populaarseim keel
ning selles osas arvatavasti lähiajal
muutusi ei toimu
JAVA on laialdaselt kasutuses
erinevate veebilahenduste loomisel
JAVA EE (Enterprise Edition)
Kogum vahendeid erinevate
lahenduste loomiseks:
Veebi rakendused
Veebi teenused
Sõnumivahetus
Andmebaasid
…
http://en.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition
JAVA EE
Kogum vahendeid erinevate
lahenduste loomiseks:
Veebi rakendused
Veebi teenused
Sõnumivahetus
Andmebaasis
…
Web Container
Servlet
JSP
http://en.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition
Web Container
Manages component
life cycles
Accepts
requests,
sends
responses
Routes requests to
applications
http://tutorials.jenkov.com/java-servlets/overview.html
Web Containers
Apache Tomcat
JBoss
WebLogic
Jetty
Glassfish
Websphere
…
Web Containers
Multiple applications
inside one container
http://tutorials.jenkov.com/java-servlets/overview.html
Application structure
Application structure
Java source files
Application structure
Document root
Application structure
Static content
15
Application structure
Configuration,
executable code
Application structure
Deployment descriptor
Application structure
Compiled classes
Application structure
Dependencies (JAR-s)
Application structure
Java Server Pages
Deployment descriptor
(web.xml)
Instructs the container how to deal with this
application
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
version="3.0">
<welcome-file-list>
<welcome-file>index.html</welcome-file>
</welcome-file-list>
</web-app>
Deployment descriptor
(web.xml)
In Servlet API version 3.0 most
components of web.xml are replaced by
annotations that go directly to Java
source code.
We will see examples later
Servlets
On JAVA klass, mis töötleb sissetulevat
päringut ning tagastab vastuse
Enamasti kasutatakse HTTP päringute ja
vastuste töötlemiseks
Servletid töötavad veebikonteineris, mis
hoolitseb nende elutsükli ning päringute
suunamise eest
javax.servlet.http.HttpServlet – abstraktne
klass, mis sisaldab meetodeid doGet ja
doPost HTTP päringute töötlemiseks
Servlet example
public class HelloServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req,
HttpServletResponse resp)
throws ServletException, IOException {
PrintWriter writer = resp.getWriter();
writer.println("<html><head><title>Hello</title></head><bo
dy>");
writer.println("<p>Hello World!</p>");
writer.println("<p>Current time: " + new Date() +
"</p>");
writer.println("</body></html>");
}
}
HttpServlet methods
For each HTTP method there is
corresponding HttpServlet method
doPost
doGet
doPut
…
Servleti töö
Servlet Mapping
Before Servlet 3.0 in web.xml
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>example.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
Servlet Mapping
In Servlet 3.0 via annotation
@WebServlet("/hello")
public class HelloServlet extends HttpServlet {
...
Servlet life cycle
http://tutorials.jenkov.com/java-servlets/servlet-life-cycle.html
Üldine servleti elutsükkel
Kui veebikonteineris puudub Servleti
instants
Laetakse Servleti klass
Luuakse isend
Initsialiseeritakse (init meetod)
Iga päringu jaoks kutsutakse välja
service meetod
Servleti kustutamisel kutsutakse välja
destroy meetod
Sessions
HTTP is a stateless protocol, but we
often need the server to remember us
between requests
There are some ways
Cookies
URL rewriting
Java HttpSession
HttpSession is a common interface for
accessing session context
Java Servlet API abstract away the
details of how the session is
maintained
Java HttpSession
http://java.sun.com/developer/onlineTraining/JSPIntro/contents.html
HttpSession example
HttpSession session = req.getSession();
int visit;
if (session.isNew()) {
visit = 0;
} else {
visit = (Integer) session.getAttribute("visit");
}
session.setAttribute("visit", ++visit);
HttpSession example
Either create a new
HttpSession session = req.getSession();
session or get existing
int visit;
if (session.isNew()) {
visit = 0;
} else {
visit = (Integer)
session.getAttribute("visit");
}
session.setAttribute("visit", ++visit);
HttpSession example
HttpSession session = req.getSession();
int visit;
if (session.isNew()) { Check if the session is fresh or not
visit = 0;
} else {
visit = (Integer)
session.getAttribute("visit");
}
session.setAttribute("visit", ++visit);
HttpSession example
HttpSession session = req.getSession();
int visit;
if (session.isNew()) {
visit = 0;
} else {
Retrieve attribute
visit = (Integer) session.getAttribute("visit");
}
session.setAttribute("visit", ++visit);
HttpSession example
HttpSession session = req.getSession();
int visit;
if (session.isNew()) {
visit = 0;
} else {
visit = (Integer) session.getAttribute("visit");
}
session.setAttribute("visit", ++visit);
Update attribute
HttpServletRequest
Contains request information
Also can be used to store attributes
request.setAttribute(“key", value);
request.getAttribute(“key”);
HttpServletRequest:
parameters
request.getParameterNames();
Enumeration<String>
String value = request.getParameter("name");
HttpServletRequest: meta
data
request.getMethod();
“GET”, “POST”, …
request.getRemoteAddr();
Remote client’s IP
request.getServletPath();
“/path/to/servlet”
…
HttpServletRequest: headers
request.getHeaderNames();
Enumeration<String>
request.getHeader("User-Agent");
“Mozilla/5.0 (X11; Linux x86_64) …”
Request Headers
Accept
Accept-Encoding
Accept-Language
Connection
Cookie
Host
User-Agent
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
gzip, deflate
et,et-ee;q=0.8,en-us;q=0.5,en;q=0.3
keep-alive
JSESSIONID=C687CC4E2B25B8A27DAB4A5F30980583;
__utma=111872281.1173964669.1316410792.1318315398.13
38294258.52; oracle.uix=0^^GMT+3:00^p
localhost:8080
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:19.0)
Gecko/20100101 Firefox/19.0
HttpServletRequest: cookies
Cookie[] cookies =
request.getCookies();
cookie.getName();
cookie.getValue();
cookie.setValue(“new value”);
Cookie
JSESSIONID C687CC4E2B25B8A27DAB4A5F30980583
C687CC4E2B25B8A27DAB4A5F30980583
utma
111872281.1173964669.13...318315398.1338294
111872281.1173964669.13...318315398.1338294258.52
258.52
oracle.uix
0^^GMT 3:00^p
0^^GMT+3:00^p
HttpServletResponse
Allows to set response information
response.setHeader("Content-Type", "text/html");
response.addCookie(new Cookie("name", "value"));
Response Headers
Content-Language
Content-Type
Date
Server
Transfer-Encoding
et
text/html;charset=UTF-8
Mon, 11 Mar 2013 06:48:54 GMT
Apache-Coyote/1.1
chunked
HttpServletResponse: content
response.getWriter().println("...");
Write text
response.getOutputStream().write(...)
;
Write binary
Problem with servlets
Writing HTML in Java is hideous
PrintWriter writer = resp.getWriter();
writer.println("<html><head><title>Hello</title></head><body>");
writer.println("<p>Hello World!</p>");
writer.println("<p>Current time: " + new Date() + "</p>");
writer.println("</body></html>");
Java Server Pages (JSP)
Write standard markup
Add dynamic scripting elements
Add Java code
JSP example
war/WEB-INF/jsp/hello.jsp
<%@page import="java.util.Date"%>
<html>
<head><title>Hello</title></head>
<body>
<p>Hello World!</p>
<p>Current time: <%= new Date() %></p>
</body>
</html>
JSP mapping
In web.xml
<servlet>
<servlet-name>hello2</servlet-name>
<jsp-file>/WEB-INF/jsp/hello.jsp</jsp-file>
</servlet>
<servlet-mapping>
<servlet-name>hello2</servlet-name>
<url-pattern>/hello2</url-pattern>
</servlet-mapping>
The JSP Model 2 architecture
http://en.wikipedia.org/wiki/JavaServer_Pages
JSP life cycle
http://www.jeggu.com/2010/10/jsp-life-cycle.html
Dynamic content
Expression
<p>Current time: <%= new Date() %></p>
Scriptlet
<p>Current time: <% out.println(new Date());
%></p>
package org.apache.jsp.WEB_002dINF.jsp.document;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import java.util.Date;
public final class testdokument_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent {
private static final javax.servlet.jsp.JspFactory _jspxFactory =
javax.servlet.jsp.JspFactory.getDefaultFactory();
private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;
private javax.el.ExpressionFactory _el_expressionfactory;
private org.apache.tomcat.InstanceManager _jsp_instancemanager;
public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
return _jspx_dependants;
}
public void _jspInit() {
_el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
_jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
}
public void _jspDestroy() {
}
public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)
throws java.io.IOException, javax.servlet.ServletException {
final javax.servlet.jsp.PageContext pageContext;
javax.servlet.http.HttpSession session = null;
final javax.servlet.ServletContext application;
final javax.servlet.ServletConfig config;
javax.servlet.jsp.JspWriter out = null;
final java.lang.Object page = this;
javax.servlet.jsp.JspWriter _jspx_out = null;
javax.servlet.jsp.PageContext _jspx_page_context = null;
try {
response.setContentType("text/html; charset=UTF-8");
pageContext = _jspxFactory.getPageContext(this, request, response,
null, true, 8192, true);
_jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;
out.write("\r\n");
out.write("\r\n");
out.write("<p>Current time: ");
out.print( new Date() );
out.write("</p>");
} catch (java.lang.Throwable t) {
if (!(t instanceof javax.servlet.jsp.SkipPageException)){
out = _jspx_out;
if (out != null && out.getBufferSize() != 0)
try { out.clearBuffer(); } catch (java.io.IOException e) {}
if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
else throw new ServletException(t);
}
} finally {
_jspxFactory.releasePageContext(_jspx_page_context);
}
}
}
Dynamic content
Declaration
<%!
private Date currentDate(){
return new Date();
}
%>
<p>Current time: <%= currentDate() %></p>
JSP Eeldefineeritud muutujad
request- HttpServletRequest
response – HttpServletResponse
out – Writer
session – HttpSession
application – ServletContext
pageContext – PageContext
JSP Märgendid
jsp:include
Veebipäring antakse ajutiselt üle mingile teisele JSP lehele.
jsp:forward
Veebpäring antakse jäädavalt üle mingile teisele JSP
lehele.
jsp:getProperty
Loeb mingi JavaBeani muutuja väärtuse.
jsp:setProperty
Määrab mingi JavaBeani muutuja väärtuse.
jsp:useBean
Loob uue või taaskasutab mingit JSP lehele kättesaadavat
JavaBeani.
Expression Language (EL)
Easy way to access JavaBeans in
different scopes
Rea summa: ${rida.summa * rida.kogus}
Basic Operators in EL
Operator
Description
.
Access a bean property or Map entry
[]
Access an array or List element
()
Group a subexpression to change the evaluation
order
+
Addition
-
Subtraction or negation of a value
*
Multiplication
/ or div
Division
% or mod Modulo (remainder)
== or eq
Test for equality
!= or ne
Test for inequality
< or lt
Test for less than
> or gt
Test for greater than
<= or le
Test for less than or equal
>= or gt
Test for greater than or equal
&& or and Test for logical AND
|| or or
Test for logical OR
! or not
Unary Boolean complement
empty
Test for empty variable values
http://www.tutorialspoint.com/jsp/jsp_expression_language.htm
Scopes
Many objects allow you to store
attributes
ServletRequest.setAttribute
HttpSession.setAttribute
ServletContext.setAttribute
Andmete skoobid
ServletContext – veebikontekst, üks
ühe rakenduse ja JVM-i kohta
Sessioon – üks iga kasutajasessiooni
kohta (erinev browser = erinev
sessioon)
Request – konkreetse päringu skoop
Andmete kirjutamiseks/lugemiseks on
meetodid setAttribute/getAttribute
Scopes
http://java.sun.com/developer/onlineTraining/JSPIntro/contents.html
Scopes
<%
application.setAttribute("subject", "Web information systems");
session.setAttribute("topic", "Servlets");
request.setAttribute("lector", "Roman");
pageContext.setAttribute("lector", "Roman");
%>
Subject: ${subject}
Topic: ${topic}
Lector: ${lector}
Väljund: Subject: Web information systems Topic: Servlets Lector: Roman
Scopes
<%
application.setAttribute("subject", "Web information systems");
session.setAttribute("topic", "Servlets");
request.setAttribute("lector", "Roman");
pageContext.setAttribute("lector", "Roman");
pageContext.setAttribute("subject", "Meie uus teema");
application.setAttribute("subject", "Meie järgmine teema");
%>
Subject: ${subject}
Topic: ${topic}
Lector: ${lector}
Mis on väljundiks?
Scopes
<%
application.setAttribute("subject", "Web information systems");
session.setAttribute("topic", "Servlets");
request.setAttribute("lector", "Roman");
pageContext.setAttribute("lector", "Roman");
pageContext.setAttribute("subject", "Meie uus teema");
application.setAttribute("subject", "Meie järgmine teema");
%>
Subject: ${subject}
Topic: ${topic}
Lector: ${lector}
Subject: Meie uus teema Topic: Servlets Lector: Roman
Scopes
<%
application.setAttribute("subject", "Web information
systems");
session.setAttribute("topic", "Servlets");
request.setAttribute("lector", "Roman");
pageContext.setAttribute("lector", "Roman"); Less visible
%>
Subject: ${subject}
Topic: ${topic}
Lector: ${lector}
JavaBeans
public class Person implements Serializable {
Implements Serializable
private String name;
public Person() {}
Public default constructor
public String getName() {
return name;
}
getX and setX methods
for each property X
public void setName(String name) {
this.name = name;
}
}
JavaBeans in EL
Person person = new Person();
person.setName("Roman");
request.setAttribute("person", person);
<p>Person: ${person.name}</p>
Java Standard Tag Library
(JSTL)
Set of standard tools for JSP
<%
List<String> lectors = Arrays.asList("Siim", "Roman", "Margus");
pageContext.setAttribute("lectors", lectors);
%>
<c:set var="guestLector" value="Margus" />
<c:forEach var="lector" items="${lectors}">
Name: ${lector}
<c:if test="${lector eq guestLector}“>(guest)</c:if>
<br />
</c:forEach>
Problem with JSP
Writing Java in JSP is hideous
<p>Current time: <%= currentDate()
%></p>
Model-View-Controller (MVC)
http://java.sun.com/blueprints/patterns/MVC-detailed.html
Servlet controller, JSP view
Controller gets invoked
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
req.setAttribute("currentDate", new Date());
Model data
req.getRequestDispatcher("/WEB-INF/jsp/hello.jsp").forward(req, resp);
}
Servlet controller, JSP view
Controller gets invoked
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
req.setAttribute("currentDate", new Date());
req.getRequestDispatcher("/WEB-INF/jsp/hello.jsp").forward(req,
resp);
Select and invoke view
}
Servlet controller, JSP view
WEB-INF/jsp/hello.jsp
<html>
...
<body>
<p>Current time: ${currentDate}</p>
View uses the
</body>
data from model
</html>
Filters
Allows you to do something before, after or
instead of servlet invocation.
Filter chain
http://docs.oracle.com/javaee/5/tutorial/doc/bnagb.html
Filter example
public class LoggingFilter implements Filter {
public void doFilter(ServletRequest request, ServletResponse
response, FilterChain chain) throws IOException, ServletException
{
long start = System.currentTimeMillis();
chain.doFilter(request, response);
long end = System.currentTimeMillis();
System.out.println("Time spent: " + (end - start));
}
}
Filter example
public class LoggingFilter implements Filter {
public void doFilter(ServletRequest request, ServletResponse
response, FilterChain chain) throws IOException, ServletException
{
long start = System.currentTimeMillis();
chain.doFilter(request, response);
Invoke next filter in
chain or the servlet
if this was the last filter
long end = System.currentTimeMillis();
System.out.println("Time spent: " + (end - start));
}
}
Filter declaration
Before Servlet 3.0 in web.xml
<filter>
<filter-name>loggingFilter</filter-name>
<filter-class>example.LoggingFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>hello</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
Filter declaration
In Servlet 3.0 via annotation
@WebFilter("/*")
public class LoggingFilter implements
Filter {
...
Life cycle event listeners
javax.servlet.ServletContextListener
javax.servlet.ServletContextAttributeListener
javax.servlet.ServletRequestListener
javax.servlet.ServletRequestAttributeListener
javax.servlet..http.HttpSessionListener
javax.servlet..http.HttpSessionAttributeListener
Listener example
public class LoggingRequestListener implements
ServletRequestListener {
@Override
public void requestInitialized(ServletRequestEvent event) {
System.out.println("Received request from " +
event.getServletRequest().getRemoteAddr());
}
@Override
public void requestDestroyed(ServletRequestEvent event) {}
}
Listener declaration
Before Servlet 3.0 in web.xml
<listener>
<listener-class>
example.LoggingRequestListener
</listener-class>
</listener>
Listener declaration
In Servlet 3.0 via annotation
@WebListener
public class LoggingRequestListener
implements ServletRequestListener
{
...
Should I bother?
• There are a lot of fancy Java web
frameworks that simplify application
building.
• Should I still learn these basic
technologies, will I ever use them?
Should I bother?
• You are still going to deploy your
application to a web container.
• Most traditional frameworks use JSP
as the view technology.
What about servlets?
• Most frameworks are based on the Servlet
API
• You will probably still encounter things like
HttpSession, HttpServletRequest etc inside your
code.
• You might want to write filters and listeners.
• You probably won’t write much servlets. But
sometimes they can still be handy for simple
tasks.
Sources of wisdom
Tutorial
http://docs.oracle.com/javaee/6/tutorial/doc/
http://docs.oracle.com/javaee/5/tutorial/doc/
API
http://docs.oracle.com/javaee/6/api/
http://docs.oracle.com/javaee/5/api/
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